When a luggage cart is pushed onto a conveyor system for transporting pedestrians such as escalators and moving sidewalks, it is desirable to lock a wheel of the cart to keep the cart stationary with respect to the moving staircase or floor. This can be automatically accomplished by providing a sensor wheel immediately next to the front wheel as proposed in DEOS No. 2 105 547. The sensor wheel consists of a disk which is supported by the pivot shaft of the front wheel so as to be moveable to a certain extent in a downward direction. Typically, the sensor wheel is also provided with a first locking arrangement which prevents the rolling of the front wheel when the sensor wheel moves downward from its normal position, and a second locking arrangement which, at the same time, prevents the steering or swiveling movement of the front wheel. Therefore, when the front wheel is pushed onto the moving staircase or floor which is normally provided with a number of longitudinal slots, the sensor wheel drops into one of such longitudinal slots whereby the first locking arrangement locks up the front wheel to keep the cart stationary on the moving staircase or floor. The second locking arrangement at the same time prevents the swiveling movement of the front wheel and keeps the front wheel at the straight ahead position. This is advantageous because it prevents the lateral swaying of the front end of the cart which could occur as the cart moves on from a descending escalator to a normal stationary floor if the front wheel consists of a caster wheel, and hangs over from an edge of the step of the escalator. When the caster wheel hangs over an edge of a step of a descending escalator, the caster wheel tends to swivel into a reverse position under the action of the gravity.
According to the previously proposed sensor wheel arrangements, there was a risk of damaging the sensor wheel when the cart is tilted sideways on a slotted floor. Conventionally, the sensor wheel was attached to one side of the front wheel, and the tilting of the front wheel, in particular toward the side of the sensor wheel, caused the sensor wheel to be wedged in the longitudinal slot of the floor involving such a great stress to the sensor wheel that a damage to the sensor wheel was highly possible.